Causes

Like many mental health disorders, several factors may contribute to development of drug addiction. The main factors are:

• Environment. Environmental factors, including your family's beliefs and attitudes and exposure to a peer group that encourages drug use, seem to play a role in initial drug use.
• Genetics. Once you've started using a drug, the development into addiction may be influenced by inherited (genetic) traits, which may delay or speed up the disease progression.

Changes in the brain

Physical addiction appears to occur when repeated use of a drug changes the way your brain feels pleasure. The addicting drug causes physical changes to some nerve cells (neurons) in your brain. Neurons use chemicals called neurotransmitters to communicate. These changes can remain long after you stop using the drug.